As effective anti-seismic measures for existing structures in general buildings, a seismic isolation retrofit method is widely used, in which an existing structure itself is seismically isolated or seismic isolation is achieved in an intermediate layer of the existing structure.
On the other hand, existing plant support structures are built putting their functions first, and it is difficult to apply the seismic isolation retrofit method for the following reasons.
Seismic isolation retrofit on a foundation requires large-scale construction on the foundation, which increases a suspension period of plant functions. Also, plant functions provided on a foundation such as an underground pit or piping may be damaged.
For seismic isolation retrofit in the intermediate layer, a floor height of one floor is as high as 10 m, which is higher than general buildings. For this reason, as shown in FIGS. 7A and 7B, if a seismic isolation device 111 is provided in an intermediate position of a column 105 between beams 107,107, the distances above and below the seismic isolation device 111 are longer than the device, which prevents bending rigidity in a horizontal direction (hereinafter referred to as horizontal rigidity) of a seismic isolation layer from being ensured. The plant support structure is typically a brace structure rather than a rigid-framed structure, and removing a brace prevents rigidity and strength of the seismic isolation layer from being ensured.
For example, Patent Literatures 1 to 3 make proposals on seismic isolation, which consider general buildings having a rigid-framed structure and are difficult to be applied to an existing plant support steel frame.
Specifically, Patent Literature 1 proposes to place concrete around a column of an existing structure except only an area in which a seismic isolation device is installed, and then cut the area of the existing column in which the seismic isolation device is installed, thereby providing the seismic isolation device. However, applying this to a plant support structure increases a length of a cast-in-place RC column part, which prevents rigidity of a seismic isolation layer from being ensured. Also, cast-in-place concrete needs to be placed over a height substantially corresponding to one floor on an outer periphery of the existing column, which requires labor and increases a suspension period of a plant.
Patent Literature 2 provides seismic isolation in an intermediate layer by securing bearing portions (3) to upper and lower outer peripheries of an area of a column of an existing structure into which a seismic isolation device is inserted and providing the seismic isolation device between the bearing portions. However, applying this to a plant support structure prevents horizontal rigidity of a seismic isolation layer from being ensured due to low bending rigidity of an existing column (1).
Patent Literature 3 proposes providing a viscous damper (8) that functions following displacement generated in a seismic isolation device in an earthquake, in a seismic isolation layer having a structure for seismic isolation provided in an intermediate layer, wherein a reaction in a lateral direction generated in the viscoelastic damper (8) in an earthquake is borne by a vertical reaction portion (6) and a lateral reaction portion (7) provided in the seismic isolation layer. In Patent Literature 3, only the reaction of the viscous damper (8) is borne by a compression force and a tensile force of the lateral reaction portion (7), and the lateral reaction portion (7) is low in strength, which makes it difficult to ensure horizontal rigidity of the seismic isolation layer.